The mechanisms by which new pathogens human pathogens emerge are of increasing relevance in the control of infectious diseases. My long-term research goal is to explore the role of biofilms in the emergence of new pathogenic strains. Vibrio cholerae O139, a recently emerged pathogenic strain, will be used as a model for this study. V. cholerae is an inhabitant of marine environments. Although biofilm formation is an integral part of its existence in this environment, little is known about the V. cholerae biofilm at the molecular level. A rapid screen for biofilm formation will be used to isolate V. cholerae O139 transposon insertion mutants that are unable to initiate and maintain biofilms. The mutants will be characterized at the molecular biological, microscopic, and molecular levels. Genes involved in biofilm formation that are unique to V. cholerae O139 among the pathogenic V. cholerae strains will be identified and studied to determine possible methods of horizontal gene transfer. My specific aims are to: (I) Isolate and characterize V. cholerae O139 mutants that are defective in initiation of biofilm formation, (II) Identify and characterize genes responsible for the maintenance of V. cholerae O139 biofilms, and (III) Identify genes involved in biofilm formation that are unique to V. cholerae O139.